Device for dewatering solid-liquid suspensions

ABSTRACT

A device for dewatering solid-liquid suspensions, in particular pulp suspensions, in which the suspension is dewatered between two belts and a dewatering zone is formed in the shape of a wedge between the two belts. The wedge height at its end closest to the outlet is adjustable over the entire belt width by an adjusting element.

This is the U.S. national stage of International Application No.PCT/EP96/04748 filed Oct. 31, 1996.

The invention relates to a device for dewatering solid-liquidsuspensions, in particular pulp suspensions, on which the suspension isdewatered between two belts, a dewatering zone being formed in the shapeof a wedge zone.

Such devices, as are known from AT 385.793, for example, have thedisadvantage of being severely limited in their production spectrum andin the obtainable dry content when producing mats with different basisweights. A fixed gap at the end of the wedge only allows a small,restricted range of basis weights. Here, a high basis weight yields ahigh dry content and a low basis weight a low dry content. If thepressure is too great at the end, particularly with pulps that aredifficult to dewater, the pulp is squeezed out at the sides. Further dueto the high pressure also the deckle sealing in the wedge zone may bedamaged. As the basis weight rises, this leads to higher pressures and,as a result, the drive power the machine requires because of thefrictional force is so great that the machine comes to a standstill.

The aim of the invention is, thus, to create a machine which alsopermits high dry content levels at high basis weights, without the pulp,particularly if it is difficult to dewater, being squeezed out at thesides or the deckle sealings being damaged, and where the risk of themachine coming to a standstill is virtually eliminated.

According to the invention, this is achieved by making the wedge heightadjustable, particularly over the entire belt width, at the wedge outletend, in particular automatically, e.g. elastically. Since the wedgeheight at the outlet end can be adjusted, the correct gap can always beset for the appropriate basis weight.

An advantageous further development of the invention is characterized bythe top section of the wedge, or alternatively the bottom section of thewedge, being adjustable, in particular automatically, e.g. elastically.With these variants, the wedge can be set at the optimum height to suitthe other structural features of the machine.

A favorable configuration of the invention is characterized by theadjustment being made using one or more pneumatic elements arranged overalmost the entire machine width, with flexible tubes or pneumaticcylinders being provided as pneumatic elements. As an alternative, theadjustment can be made using one or more hydraulic elements arrangedover almost the entire machine width, with bellows, flexible tubes orhydraulic cylinders being provided as hydraulic elements. By usingpneumatic or hydraulic elements to set the wedge height at the outletend, the gap can set itself automatically with the pressure occurring.Particularly the embodiment with flexible tubes or bellows extendingover almost the entire machine permits the wedge height to be adjustedto suit the basis weight in this way, even if the pulp is not evenlydistributed, for example if a wedge plate is slanted. By adapting toprevailing conditions, the machine also remains operative if there arebrief pressure fluctuations in the pulp or if the mat is thicker orarches in places. Thus, greater reliability of service is provided.

A favorable further development of the invention is characterized byeither the top section or the bottom section of the wedge beingspring-supported.

A favorable configuration of the invention is characterized by the topand bottom sections of the wedge being connected mechanically, inparticular adjustably, at the side of the headbox. Due to the mechanicalconnection between the top and bottom sections of the wedge on the sidefacing the headbox, corresponding influence can be exerted on thethickness of the filter cake produced and also on dewatering of the matby the existing apropriate length of the wedge zone.

A favorable further development of the invention is characterized by themaximum and minimum gap adjustment being restricted by limit stops. Bylimiting the maximum adjustment, dewatering of the material is alwaysguaranteed, whereas a restriction on minimum adjustment avoids damage tothe machine in no-load operation. The gap can be set according to thechange in the deckle sealings such that they are always operative.

A favorable configuration of the invention is characterized by the wedgezone continuing beyond the center of the first subsequent roll,particularly an S-roll, where the top or, alternatively, the bottomsection of the wedge, depending on the roll configuration, extends pastthe roll center and its opposite wedge section projects into the spacebetween dewatering belt and roll. With this design, the pulp web betweenthe belts is stabilized up to the first S-roll, which prevents fibersfrom building up upstream of the S-roll and the pulp then being squeezedout at the sides of the dewatering belt upstream of the S-module. Inaddition, the filter cake does not expand subsequently and re-wetting isthus prevented. As a result, the throughput of the dewatering device isincreased, particularly for pulps that are difficult to dewater, such aslow-freeness pulps.

The primary advantage of the invention is that it is possible to adaptwedge dewatering rapidly to different pulp grades by changing the wedgepressure, with practically no effect on the basis weight because thepress is adapted automatically to the changes in the operatingparameters, e.g. basis weight, dewaterability, while the pressure at theend of the wedge always remains the same. By preventing pulp fromescaping at the end of the wedge, particularly by means of the wedgezone extending past the center of the first S-roll, the dewatering unitis much less sensitive to fluctuations in pulp quality. If the basisweight fluctuates, the elastic wedge opening prevents jamming.

The invention will now be described in examples and referring to thedrawings, where

FIG. 1 shows a section of a dewatering machine with wedge zone,

FIG. 2 illustrates a cross-section through the line marked II--II inFIG. 1, and

FIG. 3 shows a cross-section through the line marked III--III in FIG. 2.

The dewatering device I with a wedge zone 2 and a further dewateringzone, particularly an S-zone 3, is illustrated in FIG. 1. Here, a topwire or filter belt 4 runs over a top deflection roll 6, whose positioncan be adjusted and regulated, and then over a deflection roll 7 intothe wedge formed by plates 10 and 11. The second wire or filter belt 5also runs over an appropriate deflection roll 8 and a further deflectionroll 9 into the wedge. The material to be dewatered, for example, pulp,is fed through a headbox 12 and also into the wedge. The top 10 andbottom 11 sections of the wedge are connected mechanically at the sideof the headbox using a threaded spindle 13 and the spacing between thetwo sections is adjustable. After leaving the gap, the belts 4 and 5,with the pulp web between the two, are deflected round S-rolls 21 and22, thus effecting further dewatering. The height of the top wedgesection 10 can be adjusted here using a pneumatic or hydraulic tube 14.The compressed air or hydraulic fluid is supplied through a connectionpoint 15. Stop screws 16 are used to limit the minimum and maximumadjusting distance. A slide plate 17 is provided to absorb the axialforces. Further, a support 18 is provided for cantilevering, i.e. forchanging the endless woven belts. In order to affect the direct vicinityas little as possible, a hood 19 is integrated into the top wedgesection 10 and a filtrate tray 20 into the bottom wedge section 11. Atthe end of the wedge, the top wedge section 10 has an extension piece 23which extends beyond the center of the S-roll 21. In this way, thedewatering zone is extended on the one hand, and on the other, thefibers do not build up upstream of the S-zone, thus the pulp is notsqueezed out at the sides.

FIG. 2 shows a section through the adjusting element 14'. Thisillustration shows the beam 24 for the top frame section as well as theside sections 25, 25' of the frame. The beam 24 rests on an upperprofile 26 projecting beyond a bottom profile 27, which is attachedsecurely to the bottom frame section 28. Between the top profile 26 andthe bottom profile 27 there is a pneumatic or hydraulic tube which issupplied with air or hydraulic fluid, respectively, through a connectionpoint 15. The frame section 28 securely connected to the top wedgesection 10 can thus be pressed against the top frame section 24 inaccordance with the pressure in the tube 14. The wedge height adjustsaccording to the pressures in the wedge and the pressure in the tube 14.

FIG. 3 shows a section through the line marked III--III in FIG. 2, withthe exact structure of the top profile 26, the bottom profile 27 and thetube 14 between the two, with the appropriate connections to the topframe 24 and the frame section 28 connected to the top wedge section 10.

The invention is not restricted to the examples illustrated, but canalso be used in other belt presses, such as are used in sewage sludgedewatering, for example.

We claim:
 1. In a device for dewatering pulp suspensions between twomoving belts in an adjustable dewatering wedge wherein the improvementcomprises the wedge being formed by a top plate and a bottom platedefining a wedge gap between the plates with the belts moving throughthe wedge gap then passing over a dewatering roll which rotates about acenter, wherein the device includes means for elastically adjusting thewedge gap over the entire belt width adjacent said roll, and the wedgecontinues to the roll with one plate extending to the roll and the otherplate extending beyond the center of the roll.
 2. Device according toclaim 1, wherein the top plate is adjustable automatically elastically,and the bottom plate of the wedge is fixed.
 3. Device according to claim1, wherein the bottom wedge plate is adjustable automaticallyelastically, and the bottom plate of the wedge is fixed.
 4. Deviceaccording to claim 1 wherein the means for adjusting comprises at leastone pneumatic element arranged substantially completely across the widthof the belts.
 5. Device according to claim 4, wherein at least one tubeis provided as the pneumatic element.
 6. Device according to claim 4,wherein pneumatic cylinders are provided as the pneumatic elements. 7.Device according to claim 1, wherein the means for adjusting comprisesat least one hydraulic element arranged substantially completely acrossthe width of the belts.
 8. Device according to claim 7, wherein at leastone bellow or tube is provided as an hydraulic element.
 9. Deviceaccording to claim 7, wherein hydraulic cylinders are provided ashydraulic elements.
 10. Device according to claim 1 wherein one of thetop plate or the bottom plate of the wedge is spring-supported. 11.Device according to claim 1, wherein a headbox is located adjacent aninlet end of the wedge and the top and bottom plates of the wedge areconnected mechanically and adjustably laterally of the headbox. 12.Device according to claim 1, wherein stop means are provided forlimiting the maximum and minimum gap adjustment.
 13. Device according toclaim 1, wherein the top wedge plate extends past the roll center andthe bottom wedge plate extends to the roll.
 14. Device according toclaim 1, wherein the bottom wedge plate extends past the roll center.15. Device according to claim 2, wherein the means for adjustingcomprises at least one pneumatic element arranged substantiallycompletely across the width of the belts.
 16. Device according to claim3, wherein the means for adjusting comprises at least one pneumaticelement arranged substantially completely across the width of the belts.17. Device according to claim 2, wherein the means for adjustingcomprises at least one hydraulic element arranged substantiallycompletely across the width of the belts.
 18. Device according to claim3, wherein the means for adjusting comprises at least one hydraulicelement arranged substantially completely across the width of the belts.19. Device according to claim 15, wherein one of the top plate or thebottom plate of the wedge is spring-supported.
 20. Device according toclaim 16, wherein one of the top plate or the bottom plate of the wedgeis spring-supported.
 21. Device according to claim 17, wherein one ofthe top plate or the bottom plate of the wedge is spring-supported. 22.Device according to claim 18, wherein one of the top plate or the bottomplate of the wedge is spring-supported.
 23. Device according to claim15, wherein a headbox is located adjacent an inlet end of the wedge andthe top and bottom plates of the wedge are connected mechanically andadjustably laterally of the headbox.
 24. Device according to claim 16,wherein a headbox is located adjacent an inlet end of the wedge and thetop and bottom plates of the wedge are connected mechanically andadjustably laterally of the headbox.
 25. Device according to claim 17,wherein a headbox is located adjacent an inlet end of the wedge and thetop and bottom plates of the wedge are connected mechanically andadjustably laterally of the headbox.
 26. Device according to claim 18,wherein a headbox is located adjacent an inlet end of the wedge and thetop and bottom plates of the wedge are connected mechanically andadjustably laterally of the headbox.